The external speakers attached to my m audio prokeys 88sx are no longer working. I have replaced the fuses in both but the fuses blow on power up. I then used the keyboard with a set of headphones. One of the headphone speakers now no longer works. Any ideas ? It seems the keyboard is killing any speakers attached to it.

I rather suspect IC1 TDA7293 is the cause of your problem. If this is the case you will need to check the speaker/s

e.g.

http://www.ebay.com.au/itm/Global-AC-Adapter-4-M-Audio-Prokeys-88-Stage-Piano-Charger-Power-Supply-Cord-PSU-/260991184879

This speaker at full power draws average 1.3A at 230V and 2.5A at 120V. Mackie's recommended fuses are in line with this so your fuse is actually too high a rating. It is possible you are using cheap fast blow fuses or are over-driving the speaker (which should cause the fuse to blow) These speakers are only capable of 118db sustained (@1M) so cannot be expected to cope with anything but small venues or gentle music.

If you are competent with electronics, open it up and check the fuse(s). Especially if no lights come on. If you get voltage, then check the jacks you plugged into- they may have dirty interrupt contacts. When you plug the jack in- it opens those contacts that otherwise are closed making the circuit to the cabinet's built in speaker. Contact cleaner should clean them up if that is the issue.

While it is possible there is a power supply issue, you can see that quick with a voltmeter, it is not likely you did much more than blow a fuse.- very possible if you unplugged speakers with the amp operating..

If you think you killed it- you usually still get distorted noise.

A shorted speaker cable could cause this... however, what you do is to replace the fuse BUT wire a 150 Watt lamp in series with the power input... This acts as a resetable fuse for testing. If the lamp stays lit, you still have a failure.

This is a midi lockup problem with conflict somewhere in your setup. Have you switched midi local off on the keyboard?

I have two of these. First thing check your power adapter for output. Just because LED's are on doesn't mean there is correct voltage... There is no reset button... Cycling power serves to reset it.

ALSO check the power input connector... sometimes those get intermittent and break connection due to vibration and initial current surge when turning on.

Reset the 88 by switching off --> hold the - and + buttons while turning on. Your device will reset and usually everything should be solved.

If it is brand new, it is likely "pilot error" as setting these up if you are unfamiliar with mixers can be frustrating.

There are several things that must be done to have a working system. Correct speaker cables are one and the setting of all the knobs are important...

DO NOT REPLACE FUSE. If any LED's are on, fuse is OK. If fuse blows, service the unit before replacing fuse to avoid further internal damage.

Make sure speaker cables are good.

Set the level control for the channel you are testing up AND you may need to press the "PAD" button to change the input gain. Turn up the master gain.

Depending on the source you are using, line or mic you may need to change the PAD button.

NOTE: This mixer does NOT have Phantom power and cannot be used with CONDENSER microphones requiring phantom power. You will get no audio from a condenser mic without phantom power. You must use dynamic mics with this mixer.

Try running the amp with no speaker cables connected. If it doesn't blow the fuse you know it's either your Speakon cables or the speakers themselves that are to blame (it's usually the cables)

If it still blows then there is a more serious problem with the power section.